Life sciences · Reference
What are amino acids?
Amino acids are the small molecules that link together to form proteins. There are 20 standard amino acids, and the order in which they are joined determines a protein’s structure and function.
Structure of an amino acid
Each standard amino acid has a central carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (the "R group"). The 20 standard amino acids share this core but differ in their side chains, which range from simple to complex and from water-attracting to water-repelling. These differences in side chains are what give each amino acid — and the proteins built from them — their distinctive chemical behaviour.
Peptide bonds and chains
Amino acids join together through peptide bonds, formed when the carboxyl group of one amino acid links to the amino group of the next. Repeating this creates a chain called a polypeptide.
The specific sequence of amino acids in a polypeptide is dictated by the order of codons in messenger RNA during translation. This sequence determines how the chain folds and therefore what the resulting protein does.
Essential and non-essential amino acids
Amino acids are sometimes classified by whether an organism can make them itself. Non-essential amino acids can be synthesised by the body, while essential amino acids cannot and must be obtained from the diet. This is a point of biochemistry about metabolism and is described here purely as classification; it is not nutritional or dietary advice.
Amino acids in research
Amino acids are fundamental to biochemistry and molecular biology, and their single-letter and three-letter codes provide a standard shorthand for writing protein sequences. Consistent notation and shared databases such as UniProt allow protein sequences to be recorded, compared, and reused unambiguously across research.
Key facts
At a glance
- Definition: building blocks of proteins
- Standard set: 20 amino acids
- Core groups: amino group, carboxyl group, side chain
- Linkage: peptide bonds form polypeptide chains
- Sequence set by: codons during translation
- Classes: essential (from diet) and non-essential
Common questions
FAQ
What are amino acids?+
Amino acids are organic molecules that join together to build proteins. There are 20 standard amino acids, each with a common core and a distinctive side chain, and their order in a chain determines a protein’s structure and function.
How many amino acids are there?+
There are 20 standard amino acids encoded by the genetic code and used to build proteins, distinguished by their different side chains.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
